8.2 Partition lock changes and resource queuing.

I've been working on a DSS query resource management module for Bizgres 
[1], which is currently in the code and working (Bizgres is based on 8.1.x).

...and therein lies my new problem - updating to the 8.2 codebase. The 
issue is that I have used the LockMgrLock [2] to:

1/ Manage the (resource) locks that provide the query queuing functionality.
2/ Protect shared memory structures (the queues and portal/statement 
hashes) that provide the modified conflict routines and data for the queues.


However in 8.2 the partition lock changes break this design. So I'm 
thinking of the following;

1/ Use the partition lock for the (resource) locks - as they live in the 
lock hash table along with the standard and advisory locks.
2/ Protect shared memory structures (the queues and portal/statement 
hashes) with a new lwlock (ResLockMgrLock).

This complicates the code somewhat, with what looks like a lot more 
lwlock/unlock oprations - but may actually be better for concurrency as 
we have less contention for an single lock (I think).

The other approach I wondered about was arranging for the resource locks 
and related data structures to all use an *additional* partition lock - 
which would mean faking a LOCKTAG that always hashed to 
NUM_LOCK_PARTITIONS, and using that everywhere in the resource code...

Comments welcome - as I'm scratching my head somewhat about this :-)!

Cheers

Mark



[1] http://archives.postgresql.org/pgsql-hackers/2006-07/msg00133.php
[2] The main reason that a new lwlock was not used was that we need to 
be able to do deadlock checking between resource and standard locks.
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